The present invention relates to a photographic camera having a built-in optical converter.
The photographic camera equipped with a built-in optical converter separately of the standard or main objective lens is well known to those skilled in the art. In this known photographic camera, the built-in optical converter generally serves to transmit a spatial image, formed by the standard lens, of a target object to be photographed, to a photographic film on a scale different from that of the image projected onto the film solely by the standard lens, for example, on a magnified scale, when such built-in optical converter is brought into alignment with the optical axis of the standard lens. So far as magnification is involved, this optical converter is generally referred to as a telephoto converter.
The U.S. Pat. No. 4,214,829 issued to Saichiro Ohashi, the inventor of the present invention, discloses a rangefinder camera of a type wherein the optical converter, for example, the telephoto converter is carried behind the standard lens for pivotal movement into and out of alignment with the optical axis of the standard lens. The switching mechanism employed therein is concurrently constituted by the focusing ring manipulatable to bring a target object to be photographed into focus. For enabling the telephoto converter to be selectively brought into and out of alignment with the standard lens, the focusing ring is made to rotate through spaced first and second predetermined focusing angles such that, when and so long as the focusing ring is rotated through the first focusing angle, the converter is held in position out of alignment with the standard lens, but when and so long as it is rotated through the second focusing angle, the converter is held in position in alignment with the standard lens. The converter is carried by the camera body behind the standard lens assembly by means of a support arm having a cam follower. The cam follower, for example, the roller element, protrudes through the front wall of the camera body into the standard lens assembly and terminates in engagement with a substantially eccentric cam ring rotatable together with the focusing ring while a biasing spring is also used to urge the converter towards the position out of alignment with the standard lens. The cam ring is so shaped that only when the focusing ring overrides from the capability of being moved through the first focusing angle onto the capability of being moved through the second focusing ring, the converter can be brought to the position in alignment with the standard lens by the action of the biasing spring. The standard lens is, when the converter is brought into alignment therewith, shifted a distance frontwardly of the camera from the position occupied when the converter is out of alignment therewith, thereby to compensate for change in optical system as a whole.
The rangefinder camera disclosed in the above mentioned patent is successful and effective in substantially eliminating such time-consuming and/or complicated handling procedure as the necessity of manipulating separately the focusing ring and an additional manipulatable element specifically designed for selectively bringing the converter into and out of alignment with the standard lens. However, the prior art rangefinder camera still has some problems to be solved.
By way of example, since as the converter is brought into alignment with the standard lens pivoting in the fixed plane perpendicular to the optical axis, the standard lens is shifted frontwardly of the camera thereby to separate a relatively large distance from the converter. While the frontward shift of the standard lens is necessitated to compensate for change in design of the optical system as a whole, the presence of the relatively large space between the standard lens and the converter not only makes the camera bulky, but also make it difficult to design the optical system as a whole capable of achieving a desired magnification. The increased size of the lens assembly may be minimized by carefully selecting the design of the optical system as a whole, but the lens assembly would be heavy and expensive, or the lens assembly would be susceptible to the enhanced optical aberration and/or the reduced resolution. This is also true even where the design is made to achieve the intended magnification.
In addition, the provision of the first and second angles through which the focusing ring is rotatable means that a "re-focusing" manipulation is required. That is, when a photographer while moving the focusing ring through the first focusing angle for focus adjustment has decided to use the converter and then switches the converter into alignment with the standard lens, he or she has to recommence the focus adjustment by turning the focusing ring through the second focusing angle. The consequence is that, with the prior art camera disclosed in the above mentioned U.S. Patent, the photographer may lose a decisive shutter change.